This invention relates to a hybrid vehicle provided with a combustion engine and an electric motor as a source of power.
In a parallel type hybrid vehicle, where a motor generator is connected to the output shaft of the engine, power is supplied to the motor generator and the output of the engine is thereby assisted if needed during acceleration. During deceleration and braking, fuel supply to the engine is stopped, the motor generator is operated as a generator, and the power generated is used to charge the battery (JP-A-H10-295002, JP-A-H10-252517 and JP-A-H8-275305). In a series type hybrid vehicle, only the motor generator drives the wheels and the engine drives only the generator (JP-A-H10-313505).
In the above conventional parallel hybrid vehicle, the motor generator was always operated together with the engine, namely, the vehicle cannot run by the driving force of the motor generator alone while the operation of the engine is stopped. This limits the operating range in which the motor generator can be used efficiently. In a hybrid vehicle wherein the motor generator is directly connected to the output shaft of the engine, or the drive shaft of the wheels, the rotation speed ratio between the motor generator and engine or between the motor generator and the drive shaft is fixed, so the motor generators which can be used are limited. Further, in the above-mentioned hybrid vehicles, a flywheel or vehicle wheels must have a special construction to install the motor generator, and this leads to a cost increase.
This invention is a hybrid vehicle comprising a transmission wherein the rotation speed ratio of the input shaft and output shaft is varied, a clutch which engages/disengages so as to connect/disconnect the output shaft of the engine and the input shaft of the transmission, a motor generator which functions both as a motor and a generator, a power transmission mechanism which transmits rotation between the input/output shaft of the motor generator and the input shaft of the transmission, a power storage element which stores power supplied to the motor generator, and a motor running control means which disengages the clutch according to running conditions and drives the motor generator.
In this invention, the engine output shaft and the input/output shaft of the motor generator are connected via the clutch and the transmission. Therefore, by disengaging the clutch, it is possible to stop operation of the engine in the low speed, low load region, and to run the vehicle under the power of only the motor generator. This expands the running region of the motor generator, achieves reduction of fuel consumption, improves power performance and reduces exhaust gas emissions. In this invention, as the rotation of the motor generator can be transmitted to the drive shaft of the wheels at any speed ratio, motor generators of various specifications may be used. Further, as it is unnecessary to adopt a special construction for the drive system of the flywheel of the engine or the wheels to install the motor generator, costs are reduced.
The above power transmission mechanism may be a construction wherein power is transmitted to the input shaft of the transmission by reducing the rotation of the input/output shaft of the motor generator. Hence, there is less restriction on the specification of the motor generator, and a smaller motor generator may be used.
In the hybrid vehicle of this invention, a starting-by-motor control means which disengages the clutch and drives the motor generator when the power storage amount exceeds a predetermined value and the vehicle starts, and a starting-by-engine control means which engages the clutch and drives the engine when the power storage amount falls below a predetermined value and the vehicle starts, are provided. By disengaging the clutch and driving the motor generator when there is sufficient stored charge and the vehicle starts, the engine can be stopped when the vehicle starts, and noise and fuel consumption can be still further reduced.
In the hybrid vehicle of this invention, a power source change-over means may be provided which changes over from the running state when the clutch is disengaged and the motor generator is driven, to the running state when the clutch is engaged and the engine is driven, as the vehicle speed rises. By changing over from the running state when the clutch is disengaged and the motor generator is driven, to the running state when the clutch is engaged and the engine is driven as the vehicle speed rises, sufficient power is always obtained.
In the hybrid vehicle of this invention, a brake detecting means which detects when the vehicle is braking, and a braking regeneration control means which makes the motor generator regenerate power during braking, may also be provided. By making the motor generator regenerate power when the vehicle is braking, the kinetic energy of the vehicle is effectively recovered and the load on damping devices can be mitigated.